First of all, please try upgrading JuiceboxBuilder-Pro to the latest version (v1.4.3) to ensure that any bugs which were present in previous versions but which have since been fixed are not contributing to your problem.
Instructions for downloading the latest version and for upgrading JuiceboxBuilder-Pro can be found here.
If you are trying to add many images at once, Adobe AIR may not be able to allocate enough memory for the task at hand. Even if your computer has plenty of free RAM, Adobe AIR applications are limited to around 1GB of memory allocation.
If the images you are currently trying to add to your project are much larger than images you have used in the past, then this might be a possible cause for your problem. This might account for not being able to add large batches of images at once but would not explain the maximum of 14 images. This sounds more like JuiceboxBuilder-Pro might be trying to process a corrupt image and then just gets stuck. Maybe there is a corrupt image somewhere within your batch of images. Try adding the images in a different order to see if JuiceboxBuilder-Pro always gets stuck on the same image.
Also, try installing and using JuiceboxBuilder-Lite (which comes with Juicebox-Lite) to see if the problem happens with both the Lite and Pro applications. JuiceboxBuilder-Lite and JuiceboxBuilder-Pro can be installed and run side by side on the same computer without any issues. Juicebox-Lite can be downloaded from the link on this web page.
Maybe something has happened to your JuiceboxBuilder-Pro installation which is causing the problem and a clean install might help. If all is well with JuiceboxBuilder-Lite but the problem continues with JuiceboxBuilder-Pro, then you might like to try re-installing JuiceboxBuilder-Pro from scratch.
(1) Uninstall JuiceboxBuilder-Pro.
Mac: Delete the 'JuiceboxBuilder-Pro' file from the Applications folder and empty your Trash.
Windows: Use the uninstaller in the 'Control Panel -> Programs -> Uninstall a program...' list.
(2) After uninstalling JuiceboxBuilder-Pro, please check that there are no files are left behind by manually deleting the following folders from your hard drive (if they exist):
Mac: /Users/your_username/Library/Application Support/Adobe/AIR/ELS/JuiceboxBuilder-Pro
Windows: C:\Program Files (x86)\JuiceboxBuilder-Pro
Windows: C:\Users\your_username\AppData\Roaming\Adobe\AIR\ELS\JuiceboxBuilder-Pro
Windows: C:\Users\your_username\AppData\Roaming\JuiceboxBuilder-Pro
Windows: C:\Users\your_username\My Documents\JuiceboxBuilder-Pro
You may need to show hidden files to find some of the above locations in Windows Explorer: http://windows.microsoft.com/en-gb/wind … dden-files
(3) Next, search your hard drive for the term 'JuiceboxBuilder-Pro' and delete any and all entries found (to be absolutely sure that nothing remains).
(4) Reinstall JuiceboxBuilder-Pro following the instructions here.
If you continue to experience difficulties, then it might help if I could see the problem for myself. If you like, please zip your images, upload the zip file somewhere and provide a download link so that I can try to replicate the problem myself and hopefully help further.
Also, please let me know exactly what happens when you say "it's only allowing me to add images by dragging them one at a time". Do you see any error messages on screen? If so, what do they say?